Respiratory disorders during sleep include sleep apnea (cessation of breathing) and hypopnea (abnormally slow or shallow breathing). Sleep apneas are among the most common chronic disorders in adults, and can cause excessive day time sleepiness and can increases risks for cardiovascular diseases.
Studies have indicated that both sleep apnea and hypopnea have serious health consequences, including an association with cardiac arrhythmias and congestive heart failure (CHF). The majority of a normal sleep pattern is non-rapid eye movement (NREM) sleep and a minority of a normal sleep pattern is rapid eye movement (REM) sleep. NREM sleep is a state of cardiovascular relaxation, reflected in an increase in vagal activity and a decrease in metabolic rate, sympathetic nervous system activity, heart rate, cardiac output, and systemic vascular resistance. REM sleep involves intermittent surges in sympathetic discharge, heart rate, and blood pressure. Many patients with heart failure have obstructive sleep apnea and/or central sleep apnea, both of which disrupt the normal relaxing effects of sleep on the cardiovascular system, and can result in intermittent apnea-induced hypoxia, hypercapnia, surges in central sympathetic outflow and afterload, daytime hypertension, and loss of vagal heart rate regulation, which can stimulate myocyte necrosis and apopsis, myocardial ischemia, arrhythmias, adverse cardiac remodeling and accelerated disease progression in heart failure. Obstructive sleep apnea and heart failure both adversely impact sympathetic nervous activation and vagal withdrawal of the cardiovascular system in general, and both detrimentally alter loading conditions and hypoxia on the ventricle.
Efforts for treating sleep disordered breathing have included continuous positive airway pressure (CPAP), atrial overdrive pacing, and CRT pacing. Other proposed methods for treating sleep disordered breathing include the stimulation of motor nerves and direct stimulation of the muscles of the upper airway.